Many dental or medical procedures, such as cleaning a root canal, require the dental/medical practitioner to know the location of the apex of a patient's tooth. The apex is the location of the tooth's root where nerve, vascular and other tissue leave the jawbone and enter the tooth's root canal and is commonly referred to as the apical foramen. These dental/medical procedures typically involve inserting a file or other tool into the root canal of a patient's tooth to remove tissue from the canal. If the dental/medical practitioner does not insert the file or other tool to the apical foramen, nerve, vascular and other tissue can remain in the tooth's root canal. This remaining tissue can become infected and create more problems for the patient. If the dental/medical practitioner penetrates the apical foramen, healthy nerve, vascular and other tissue can be damaged. Such damage can cause unnecessary pain for the patient. Consequently, a number of methods and devices currently exist to help the dental/medical practitioner determine the location of the apical foramen of a specific tooth.
One such method and device includes taking numerous radiographs, such as x-rays with an x-ray machine, of a patient's tooth while the dental or medical practitioner moves a dental tool in the root canal. Unfortunately, this method has some drawbacks. This method subjects the patient to multiple exposures of radiation as the dental or medical practitioner moves the dental tool toward the apical foramen. This method can also be very time consuming because the dental or medical practitioner does not move the dental tool while the patient's tooth is radiographed and the radiographs developed. This method can also fail to show the location of the apical foramen relative to a dental tool if the tooth cannot be isolated on a radiograph.
Another such method and device includes electronically detecting the apical foramen's location by measuring changes in impedance between an electrode in a patient's tooth (often the tool) and an electrode attached to the patient's lip. Typically, a stimulus voltage applied across these electrodes includes two or more signals. One signal has a high frequency while the other signal has a lower frequency. By monitoring the changes in the impedance associated with each signal as the dental or medical practitioner moves the tool in the root canal, the dental or medical practitioner can obtain an approximate location of the tooth's apical foramen relative to the tool.
While this generally solves the problems associated with using radiographs, this method also has some drawbacks. Abnormal teeth, such as teeth with one or more lateral or accessory canals that also extend between a tooth's root canal and the surrounding jawbone, teeth with fillings, tooth decay and no apical constriction can cause negligible or unpredictable changes in impedance when the stimulus voltage is applied to the electrodes. Thus, such methods and devices can provide the dental or medical practitioner with significantly incorrect information about the location of the apical foramen relative to the tool. In addition, variations in each applied signal can cause an impedance response that incorrectly identifies the relative location of the apical foramen.
Thus, there is a need for an apical foramen locator that can quickly and accurately identify the location of a tooth's apical foramen.